The present invention relates to a cooling apparatus, in particular, but not exclusively, to a cooling apparatus for cooling an electrical device.
The invention relates more particularly to electrical devices which perform a processing or memory function, such as any processor (for example a semiconductor or other logic device, an integrated circuit, a microprocessor and the like) or any storage device (for example a mass storage device). Such devices may be in the form of an integrated circuit, possibly mounted on a printed circuit board (PCB). Accordingly, the electrical device may be for electrical equipment, which may typically be a computer, modem, switch, hub or like equipment.
Electrical devices usually generate heat during use. During use, the device may become warm. It is undesirable for the device to become too hot because excessive heat can cause damage to components of the device.
It is known to cool electrical devices in electrical equipment using one or more fans and indeed a cooling fan is often provided in electrical equipment. In a conventional arrangement, electrical devices are arranged within a casing, the fan sucks air through one or more vents in the casing, the air passes over the devices and out of the casing via the fan.
To improve the cooling, heatsinks may be provided on the upper surface of the devices to draw heat away from the device. Conventionally, such heatsinks comprise one or more metal formations attached to the top of the device. The heatsink may comprise vertical fins attached to the upper surface of the device.
However, under many conditions, such arrangements have been found to be inefficient.
It is an object of the present invention to improve the cooling of the electrical device and/or to improve the efficiency of the cooling. One benefit of improving the efficiency of the cooling is that smaller and/or fewer fans could be used to obtain the desired cooling effect.
Furthermore, it has been realised pursuant to the present invention that, in many situations, some of the devices in an item of electrical equipment require more cooling than other devices. In order to cool such equipment sufficiently, a high air flow through the equipment is required. Other devices which require little or no cooling are also subject to the high air flow unnecessarily.
According to a first aspect of the present invention, there is provided a cooling apparatus for cooling an electrical device using a flow of coolant, the apparatus comprising a cooling unit for contact with the device, the cooling unit including a channel for transporting the coolant past the device.
By providing a channel for the flow of coolant past the device, the cooling of the device may be controlled, and can be made more efficient. Thus the efficiency of the cooling apparatus may be increased.
As used herein, it should be understood that the term xe2x80x9cchannelxe2x80x9d should be interpreted broadly to include any passage or channel along which the flow of the coolant may be directed. The term is not restricted to fully enclosed structures (as for example a tube), but also includes structures which are not fully enclosed. The flow of the coolant might be enclosed only on three sides or on two sides: the channel may comprise three surfaces or only two surfaces. It is envisaged that the channel may only comprise a single surface but that surface may serve to effect the desired flow of coolant.
Preferably, the channel comprises an enclosed structure, for example a tube or passageway. Preferably the flow of coolant is enclosed on at least three sides within the channel. In some embodiments of the invention, it will be preferable for the flow of coolant to be enclosed on all sides within the channel.
Preferably, the cooling unit is adapted to increase the flow velocity of the coolant past the device. By increasing the flow velocity, the rate and thus efficiency of cooling of the device can be increased. Thus the same cooling of the device can be achieved using fewer and/or smaller coolant devices, for example fans.
In a preferred embodiment of the invention, the sectional area of the channel varies between the inlet and the outlet of the channel. As the sectional area decreases, the velocity of the coolant, and thus its cooling effect increases.
The sectional area of the channel may decrease linearly from the inlet. Alternatively, a constriction may be formed in the channel, for example corresponding to an area of the device which requires greatest cooling.
Where the area of the channel is reduced in such a way, preferably the channel further includes a diffuser at the outlet of the channel to recover the pressure head and thus improve efficiency. The diffuser is a passage which gradually increases in sectional area downstream and its function is to reduce the velocity of the coolant to recover its head, or at least to attempt to retain the head.
The term xe2x80x9csectional areaxe2x80x9d preferably refers to a transverse cross section of the channel being substantially perpendicular to the direction of the flow of coolant at that location. Furthermore, unless clear to the contrary from the context xe2x80x9clengthxe2x80x9d preferably refers to a distance substantially parallel to the direction of flow of the coolant, and width preferably refers to a dimension being substantially perpendicular to the xe2x80x9clengthxe2x80x9d and parallel to the upper surface of the device, where appropriate.
Preferably, the cooling unit comprises a directing formation for directing the coolant towards the device. By directing the coolant towards the device, the cooling of the device can be increased.
The directing formation may be provided by a wall of the channel or may include a separate formation, which may be located in the channel or outside the channel.
Preferably, the directing formation comprises a directing surface, the surface being adapted to be angled relative to the direction of the coolant flow. Thus the coolant flow is deflected towards the device, thus increasing the efficiency of the cooling.
Preferably, the directing surface is adapted to be at an angle of between 5xc2x0 and 85xc2x0 to the direction of the coolant flow. In a preferred embodiment, the angle is between 5xc2x0 and 10xc2x0. The angle may be less than 45xc2x0, 30xc2x0 or 15xc2x0.
The directing surface may comprise a planar surface or may be curved, depending on the size and type of device to be cooled. A curved directing surface will usually be preferred having regard to the flow of the coolant through the channel. Furthermore, the shape of the directing surface can be adapted so as to direct coolant to specific hot areas of the device.
The size of the cooling unit will be chosen having regard to the size of the device or devices to be cooled. In some embodiments, the height of the cooling unit will be similar to the width of the cooling unit. The width of the cooling unit will, for some embodiments, be chosen to be the same as that of the device to be cooled.
Alternatively, the cooling unit may be smaller than or larger than the device; the cooling unit may extend beyond a surface of the device in one or more directions. Indeed, the cooling unit may extend over more than one device.
Preferably, the apparatus further includes a turbulence formation for generating turbulent flow of the coolant. Turbulent flow gives improved heat transfer from the device and therefore increased cooling. Turbulence may be effected, for example, by increasing the velocity of the coolant flow and/or providing raised areas on the surfaces of the channel. The turbulence may be localised in specific regions of the channel. The turbulence formation may comprise one or more protrusions.
Preferably, the apparatus further includes cooling fins. The cooling fins can increase the turbulence of the coolant flow. Furthermore, the cooling fins provide an increased surface area of the cooling apparatus and thus improved convection of heat from the apparatus. Cooling fins are preferably provided on the inner and/or the outer surfaces of the channel.
Preferably, the walls of the channel are profiled to increase their surface area.
In a preferred embodiment of the invention, the cooling unit is adapted to contact only one device. Thus close control of the cooling of each device of an item of electrical equipment can be effected, with each device receiving only enough cooling. Thus the efficiency of the cooling can be increased.
In alternative embodiments, the cooling unit straddles more than one device. In such arrangements, the cooling unit preferably contacts more than one device.
The cooling apparatus may comprise a plurality of cooling units, each for contact with a separate device. In preferred embodiments of the invention, the cooling units are adapted so that, in use, they cooperate, preferably so that the air flow passes from one cooling unit to the next. Thus the cooling units preferably form a duct passing over the devices.
Preferably, the channel has a flat base. The width of the base of the channel is preferably chosen to be at least 20%, and preferably at least 40%, 50% or 60% of the width of the device to which the cooling unit is to be attached. The flat surface enhances the cooling of the device.
Preferably, the cooling unit is adapted to contact at least 50% of the upper surfaces of the device. Preferably the cooling unit contacts at lest 60%, 70%, 80% or 90% of the upper surface of the device. The cooling unit may contact all of the upper surface of the device. Greater contact area can lead to greater cooling.
Where reference is made herein to xe2x80x9cupperxe2x80x9d, xe2x80x9clowerxe2x80x9d and similar expressions, preferably it refers to an arrangement in which a device is attached on the top surface of a circuit board and its upper surface is substantially horizontal. It will be appreciated that circuit boards can, in practice, be mounted xe2x80x9csidewaysxe2x80x9d or xe2x80x9cupside-downxe2x80x9d and that in such arrangements, for example, the xe2x80x9cupperxe2x80x9d surface of the device will, in fact, be its lowest surface.
Where the apparatus comprises suitable thermally conductive material, heat can flow from the device to the cooling apparatus by conduction, thus increasing the efficiency of cooling of the apparatus. Where the device comprises a chip on a circuit board, preferably the whole of the upper surface of the device is covered by the apparatus. By increasing the area of contact of the cooling unit and the device, the cooling by conduction is increased.
Preferably, the apparatus includes an attachment formation. Preferably the attachment formation is adapted for attaching the cooling unit to the device. Alternatively, the attachment formation is adapted to attach the cooling unit to the PCB or other part of the equipment, for example the casing (or duct). A formation may be provided in the equipment for cooperation with the attachment formation, for example a holder mounted on the PCB. Thus the cooling unit may include an attachment formation, or the attachment formation may be provided by another part of the equipment.
It is envisaged that the cooling apparatus could be attached to the device using adhesive. However, it is thought that in some situations, the use of adhesive may be inappropriate, for example where the device is subject to vibration. Preferably, the attachment formation includes a clip for attaching the cooling unit to the device. The attachment formation may include a resilient protrusion, for example for engagement with a corresponding indent on a surface of the device.
In an alternative embodiment, the cooling unit is attached to the circuit board.
Preferably, the apparatus includes a resilient portion for contact between the cooling unit and the device. Thus the contact, and thus heat transfer between the device and the apparatus can be increased. In a preferred embodiment, the cooling unit includes a resilient contact portion for contact with the device. When the cooling unit is attached to the device, the contact portion is biassed towards a surface of the device, thus improving thermal contact.
Preferably, the cooling unit comprises a heatsink. As indicated above, it is advantageous for heat to be removed from the device by conduction to the cooling apparatus.
Preferably, the apparatus comprises conductive plastics material.
That feature is of particular importance and thus the invention further provides cooling apparatus for cooling an electrical device using a flow of coolant, the apparatus comprising a cooling unit for contact with the device, the apparatus comprising conductive plastics material.
The thermal conductivity of the material is preferably at least 1 W/mK. In preferred embodiments, the thermal conductivity is preferably between 1 W/mK and 20 W/mK. Preferably the thermal conductivity is less than 20 W/mK, 15 W/mK, 10 W/mK or 5 W/mK. That thermal conductivity is surprisingly low for a material to be used for a heatsink. Conventionally, heatsinks comprise high thermal conductivity materials, for example steel or aluminium. Aluminium has a thermal conductivity of about 200 W/mK, and copper about 400 W/mK. It is envisaged that such conventional materials could be used for the heatsinks described herein; such heatsinks can be manufactured, for example, by extrusion, machining or casting. Preferably, however, filled plastics material is used to form the cooling units. While the materials have low conductivity, the conductivity has been found to be sufficient to give acceptable conduction from the devices. Furthermore, the materials are light and can be easy to injection mould into complex shapes.
The thermally conductive plastics material is the preferred material for the heatsinks, however, because it can be injection moulded. All of the examples of heatsinks described below can be injection moulded in one piece, thus giving lower manufacturing costs for mass production. The use of plastics materials has also been found to give great flexibility and potential for different heatsink shapes and fixing arrangements.
Preferably, the apparatus is formable in one piece, preferably by injection moulding. Preferably the cooling unit is formable by injection moulding in one piece. While it is envisaged that the cooling units can be made in several pieces and subsequently joined, the cost of manufacture and assembly of the cooling apparatus can be reduced if a one-piece cooling unit is used.
By forming the cooling apparatus of conductive plastics material, the cooling apparatus can be moulded, in particular injection moulded while still being sufficiently thermally conducting to conduct heat away from the device at an acceptable rate.
In a preferred embodiment, the apparatus comprises a composite material including a material having a relatively higher thermal conductivity in a matrix of a plastics material having a relatively lower thermal conductivity. The conductive plastics material preferably comprises a filled plastics material, preferably a filled resin. Preferred plastics include polypropylene. The filler may include a metallic material, for example aluminium, steel or ferrite, and/or may include a non-metallic material for example graphite or a ceramic material.
Preferably the material includes at least 40%, 50%, 60% or 70% of the filler by weight. Materials including about 40% by weight of the filler material are particularly preferred.
The shape of the particles of the filler material is thought to be important from a consideration of the transfer of heat in the material. It is thought that generally spherical particles of filler material would give the desired even heat transfer. Long fibres of filler material might give undesirable directional heat transfer. However, in some cases, directional heat transfer may be desirable.
In a preferred embodiment of the invention, short fibres of filler material are used, preferably having a length of less than 1 mm, 0.5 mm or 0.2 mm. The width of such particles might be about 0.01 mm. The preferred aspect ratio of the particles is less than about 100, 50 or 10.
Alternatively or in addition, the apparatus may comprise a thermally conductive coating. For example, the apparatus may comprise a material having a low thermal conductivity (which is chosen, for example, for ease of moulding of the apparatus) and including at least a partial coating of a material having a higher thermal conductivity. The coating may include a metallic coating.
Preferably, the cooling unit comprises conductive plastics material. Thus heat from the device is lost by conduction to the cooling unit, thus cooling the device.
Preferably, the cooling unit comprises a channel and the walls of the channel comprise conductive plastics material. Thus heat from the device moves by conduction into the walls of the channel where is it lost by convection in the coolant flow.
Thus it will be seen that the cooling of the device is improved.
The invention also provides cooling apparatus for cooling an electrical device using a flow of coolant, the apparatus comprising a formation for modifying a flow of coolant past the device.
Preferably the cooling apparatus further comprises a duct for transporting coolant past the cooling unit and the device.
The duct may, for example, simply comprise a space through which the coolant may flow, for example between the PCB on which the device is mounted and the equipment casing. Alternatively, or in addition, a separate passageway may be provided, for example by using one or more baffles.
Preferably the sectional area of the duct varies along its length. Thus the flow of coolant can further be controlled by selecting the shape of the duct. For example, the duct may include constrictions, at which the velocity of the coolant flow, and thus the cooling, is increased. Thus, for a particularly xe2x80x9chotxe2x80x9d device, the device could be provided with a cooling unit and, furthermore, be located in the region of the constriction in the duct so that the velocity of the coolant flow over the hot device is much increased, giving a high rate of cooling.
Preferably, the apparatus comprises a plurality of cooling units in the duct.
Preferably the apparatus further comprises a fan.
Where reference is made herein to the use of a fan, that term is to interpreted broadly to include all devices suitable for effecting flow of the coolant.
Preferably the coolant is air. It is, however, envisaged that other fluids could be used. For example, the coolant could comprise water or benzene. A suitable apparatus for effecting the flow of coolant would be used.
Preferably, the fan is arranged to suck air through the duct. It is thought that the sucking of air through the duct gives better flow of the air than would be obtained than if the fan were arranged to blow air through the duct.
Preferably, the apparatus further comprises a plurality of electrical devices.
The invention further provides electrical equipment comprising a cooling apparatus as described above.
The invention further provides a method of cooling an electrical device using a flow of air, using a cooling apparatus as described above.
Apparatus features may be applied to the method features and vice versa. The various features of the different aspect of the invention may be applied interchangeably to other aspects of the invention. Furthermore, each feature disclosed in the description, the claims and/or the drawings may be provided independently or in any appropriate combination.